By Nicholas Bakalar

Published: April 24, 2007

Helicobacter pylori, the main cause of peptic ulcer disease, might have a beneficial effect in reducing the risk of asthma and allergies, a study published yesterday suggests.

Researchers questioned 7,663 men and women about their history of asthma, allergic rhinitis and allergy symptoms, and tested them for antibodies to H. pylori. They also administered skin tests using 10 standardized allergens.

Over all, there was no association between the presence of H. pylori and current asthma status. But subjects under 43 who were colonized with the most virulent strain of H. pylori, called cagA, were 32 percent less likely to have asthma, 35 percent less likely to have allergic rhinitis and 20 percent less likely to report allergy symptoms than those who did not carry the bacterium. These subjects were roughly one-third less likely to have skin sensitivity to five common pollen plants and to Alternaria alternata, a mold.

According to the article, which appears in the journal Archives of Internal Medicine, H. pylori acquisition in industrialized countries has been diminishing with each succeeding generation for at least the past 60 years.

''Helicobacter was once ubiquitous,'' said Dr. Martin J. Blaser, a co-author of the article and the chairman of the department of medicine at New York University. ''We provide evidence that there is a relationship between the decrease in helicobacter prevalence and the increase in childhood asthma.''

The researchers noted that their observations were consistent with the ''hygiene hypothesis,'' which suggests that childhood infections, particularly infections of the gut, help diminish or prevent allergies and asthma.